Stock-Based Compensation - Summary of Weighted Average Grant-Date Fair Value of Common Stock Units and Share Awards Granted and Total Fair Value of Common Stock Units and Share Awards Vested (Detail) - Common Stock Awards [Member] - Non-Employee Director Fee Plan [Member] - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted, Shares	32	32
Weighted average grant-date fair value	$ 29.04	$ 24.70
Fair value of vested	$ 410	$ 370